Butadiene rubber may be produced utilizing catalysts of the Ziegler Natta type or by anionic lithium initiators. Ziegler Natta (Z/N) catalysts are generally preferred for producing high cis polybutadiene. An active Z/N catalyst system comprises a transition metal or Rare Earth compound and at least one or two co-catalysts. Rare Earth compounds suitable of forming active Z/N catalysts are Rare Earth carboxylates. Rare Earth carboxylates have several benefits for the butadiene formulator in that they have relatively high solubility in hydrocarbons, a polymerization medium, and reduced air sensitivity in comparison to Rare Earth alkoxides, for example.
In the world market, there are several applications for butadiene rubber. These include the production of tires, high impact polystyrene, shoe soles and golf balls. The production of tires is the major application. In tires, a high cis butadiene rubber can provide for higher abrasion resistance and a low heat build-up of tire treads, higher crack growth resistance in the side walls of radial tires, and lower rolling resistance. The production of polybutadienes with high cis isomer content is of greater interest today in view of potential shortages of natural rubber. Rare Earth carboxylates with the ability to enhance the production of high cis polybutadiene are needed. The object of this invention is to provide such a Rare Earth carboxylate.
Currently, Rare Earth carboxylates are produced and provided to the formulator in solvent, typically an organic solvent. The production of concentrated Rare Earth carboxylate liquids with long chain (C6 to C32), branched carboxylic acids is a very desirable goal in view of the beneficial reduction in commercial storage and shipping costs and the technical benefit of providing an active material in less solvent. Such a material would be easier to handle and ship. Additionally, it would provide greater flexibility for the formulator.
The concentrated Rare Earth carboxylate liquids would provide greater than 4.5% Rare Earth elements and preferably still be stable under normal storage and use conditions. Concentrated Rare Earth carboxylate liquids would preferably provide equivalent stability to commercially available Rare Earth carboxylate solutions. Instability is demonstrated by precipitation and/or a foggy or hazy appearance and/or an increase in viscosity.
The object of the present invention is to provide concentrated Rare Earth carboxylate liquids comprising from greater than about 4.5% to about 20% Rare Earth elements by weight. Preferably, the liquid has a viscosity of less than about 300 cps.